1. Field of the Invention
The present invention relates to a cut-wire type ferrous shot for shot-blasting.
2. Description of the Related Art
Shot-blasting is a process in which a plurality of ferrous shots are projected to contact ferrous objects at a high speed. Conventionally, shot-blasting has been carried out to remove sand, burrs, and scales from ferrous objects such as castings.
Ferrous shots are made to have a hardness of about Hv 400 to 500 by quenching and tempering ferrous particles produced by an atomization method. The atomization method produces conventional ferrous shots which contain dendritic structures and shrinkage cavities. These dendritic structures and shrinkage cavities promote unavoidable defects within the ferrous shots which cause the ferrous shots to be broken easily. Therefore, the atomization method produces conventional ferrous shots which vary widely in particle size.
Recently, a technique for producing ferrous shots having a hardness of Hv 400 to 500 has been developed. This technique involves serially cutting a steel wire material made of hard steel at a designated length. Therefore, this technique of producing ferrous shots is referred to as a cut-wire type method. Further, a ferrous shot produced from a cut-wire type method is referred to as a cut-wire type shot. Ferrous shots produced by the cut-wire type method are more difficult to break in comparison with the conventional ferrous shots produced by the atomization method. This is due to the presence of forged flows in the cut-wire type shot. Forged flows are formed due to drawing of the steel wire material during the cut-wire type method.
The above-mentioned conventional ferrous shots harden easily due to work-hardening as projection frequency of shot-blasting is increased. As the ferrous shots are used more often and for longer periods of time, the hardness of the ferrous shots increases. This increase in ferrous shot hardness results in an increase in the abrasion of parts mounted onto a shot-blasting machine. Therefore, the parts mounted on the shot-blasting machine require frequent periodical exchange and/or replacement.
The above-mentioned conventional ferrous shots have a high hardness; and therefore, the above-mentioned methods of producing such shots do not prevent the shots from being broken during their projection in shot-blasting. Consequently, the ferrous shots must be consumed and disposed of at a faster pace due to their destruction. Further, the surface layer of the ferrous objects is easily hardened due to work-hardening due to being beaten repeatedly by the ferrous shots during shot-blasting. Finally, there is a limit in the life of tools used for cutting the hardened ferrous objects.
The overall aim of the present invention is to improve the above-mentioned difficulties related to shot-blasting with ferrous shots.
One object of the present invention to provide a cut-wire type ferrous shot and a process of using a cut-wire type ferrous shot which can decrease the frequency of exchanging and/or replacing the parts mounted on a shot-blasting machine.
Another object of the present invention is to decrease the consumption of ferrous shots during shot blasting.
Another object of the present invention is to increase the life of tools used for cutting ferrous objects.
One object of the present invention is to suppress the abrasion of parts mounted onto a shot-blasting machine while the ferrous shots retain their function of removing foreign material that adhere to ferrous objects. Such foreign material includes sand, burrs, or scales, for example. Such ferrous objects include castings, for example.
Another object of the present invention is to provide ferrous shots having a hardness that is equivalent to, or slightly harder than, the ferrous objects. Such ferrous shots can be cut-wire type ferrous shots having a hardness of Hv 200 to 300.
Another object of the present invention is to provide ferrous shots that have a tendency to hardly be broken; and therefore, suppress abrasion of the ferrous objects.
Another object of the present invention is to provide a ferrous shot, having a hardness of Hv 200 to 300 and a low work hardening ability, for use in shot-blasting. Such ferrous shots are made by cutting a wire material.
In the present invention, xe2x80x9cblastingxe2x80x9d means both shot-abrading and shot-peening.
Since the shot concerning the present invention has a hardness of Hv 200-300, it can suppress abrasion of parts mounted to the inside of a shot-blasting machine. In addition, the ferrous shot of the present invention tends to resist being broken, thereby decreasing their consumption during the process of shot-blasting. Further, the ferrous shot has a hardness of Hv 200-300, thereby suppressing damage to tools for cutting the ferrous objects, such as casting, after shot-blasting. Therefore, the life of tools used for cutting ferrous objects is increased. Finally, the ferrous shot of the present invention can reduce industrial wastes, thereby improving a working environment.
A process of using a cut-wire type ferrous shot for shot-blasting according to the present invention comprises the steps of:
(1) Preparing cut-wire type ferrous shots for shot-blasting and a ferrous object. The cut-wire type ferrous shots having a hardness of Hv 200 to 300 and a low work hardening ability are made from cutting a wire material. The ferrous object has a foreign material thereon; and
(2) projecting the ferrous shots to the ferrous object to remove the foreign material from the ferrous object; wherein work-hardening is suppressed in both the shots and the ferrous object.
The present invention uses the shots having a hardness of Hv 200-300; and therefore, can suppress abrasion of parts mounted onto a shot-blasting machine. Since the shot used according to the present invention tends to not be broken during shot-blasting, the process according to present invention can decrease the consumption of the shots effectively. Further, the process according to the present invention can reduce industrial wastes, thereby improving a working environment. Finally, the process according to the present invention can suppress damage of a tool for cutting the ferrous objects, such as casting, after shot-blasting. Therefore, the process can lengthen the life of the tool.
The cut-wire type ferrous shots have a low average hardness of Hv 200-300 as measured by a micro Vickers hardness tester. An upper limit of the hardness may be, for example, Hv 290, Hv 280 or Hv 270: a lower limit of the hardness may be, for example, Hv 210, Hv 220 or Hv 230. Generally, the hardness from the surface layer to the center portion in a shot is almost equivalent and the above-mentioned shot is set in such a hardness range. The metal structure of the shot is generally ferrite. An area ratio of ferrite can be, for example over 90%, 95% or 98%. However, the area ratio of ferrite is not limited to these values.
The present invention is not limited in the size of the shot. The size of the shot can be set at about 0.5 mm-3 mm, for example. A plurality of cut-wire type shots are produced by serially cutting the steel wire material having an extended length. Prior to use, the shots produced by the cut-wire type method are projected in the shot-blasting machine, thereby providing a ferrous shot with an edge that is rounded in shape. According to the present invention, it is easy to provide a ferrous shot with an edge that is rounded in shape because the shot does not have a high hardness.
The shots concerning the present invention are formed of an iron-carbon alloy. The ferrous shots formed of an iron-based alloy may contain, for example, 0.03-0.15% carbon, and preferably 0.04-0.08% carbon. The ferrous shots formed of an iron-based alloy may contain, for example, less than 0.2% carbon, preferably less than 0.15% carbon, more preferably less than 0.1% carbon, most preferably less than 0.08% carbon, or, especially most preferably less than 0.05% carbon. Therefore, mild steel wire material can be used as a raw material for the shots according to the present invention because such shots reduce the work-hardening ability in a ferrous alloy. The percentages recited herein and above are in terms of a weight ratio.
Also, the ferrous shots formed of an iron-based alloy may contain 0.10-0.40% aluminum (Al), preferably 0.20-0.32% aluminum by weight ratio. An addition of aluminum (Al) can suppress age-hardening after producing the shot. Further, the alloy may contain 0.01-0.04% silicon (Si). Moreover, the alloy may contain 0.10-0.40% manganese (Mn). The ferrous shots formed of an iron-based alloy according to the present invention may contain 0.005-0.030% phosphorus (P) and 0.010-0.030% surfer (S). Generally, the shots produced by a cut-wire type method of the present invention possess less oxide film in comparison with the shots produced by a atomization method.
The process according to the present invention can use a ferrous object having a hardness less than Hv 200, for example a hardness of Hv 150-180.